In other words, it's best to wait at least until you're comfortable with each other and have a better picture of what each person wants in the relationship. But when it comes to how much time that takes, it depends.

Here's what three different researchers have to say:

Option 1: Give it a few weeks

According to Goldsmith, a total of 36 hours spent together is all it takes to be ready. Those hours don't have to be consecutive, he said — it could be a dinner date plus a weekend afternoon spent together, and so on, until the hours add up. For most people, that would probably take a few weeks.

If a couple waits much longer than that, he says, the strong desire to have sex may begin to subside. There's data to back him up — a 2012 study on sexual desire found that after the beginning phase of a relationship, sexual desire can drop.

Option 2: Hold off for a few months

Based on the findings of several studies, Coleman suggests that at least three months into a relationship — or when it's clear the honeymoon phase is over — is the best time to start having sex.

The honeymoon period is the first few months of a new relationship, when feelings of attraction are intense and it seems as if the person you're with can do no wrong.

"You move past that, and your feet are more on the ground," Coleman said, adding that [Metts' study] suggested the couples who "waited until that level fared a lot better than people who had sex on the first, second, or third date."

Goldsmith disagrees, though — he thinks the time after the honeymoon period is too late.